We have studied the incidence of congenital cytomegalovirus (CMV) infection in Japan.Currently, out of 7,995 neonates, 31 (0.39%) were identified as having congenital infection on the basis of viruria at birth. Three of 31 infected infants were symptomatic and died from generalized infection. The remaining 28 infants were all asymptomatic and showed no developmental abnormality nor sensorineural hearing loss. Maternal serum samples at 10 and 22 weeks of gestational age were available from six cases of congenital CMV infection.Serum levels of cell free soluble interleukin-2 receptor (sIL-2R) and interferon (IFN)-gamma of 6 pregnant women were determined by ELISA.Serum activities of IL-4 and tumor necrosis factor (TNF)-alpha were not detected. IgG antibody to CMV was detected from all 6 women and IgM antibody was detected from one. Meaningful rise of serum IgG-antibody titers was occurred in three cases. Serum IFN-gamma activities were detected from all 6 cases. Serum cell free sIL-2R activity rose than normal range in one IgG and IgM antibody-positive and three IgG antibody-positive woman. It is likely that serum levels of cytokines such as sIL-2R and IFN-gamma are related to the reactivation of CMV during pregnancy. Assessment of the changes of serum cytokines in CMV antibody-positive pregnant women may be useful for the prenatal diagnosis of active CMV infection during pregnancy.